1. Technical Field
The invention generally relates to electronic devices, and more specifically, a semiconductor memory device and an erasing method thereof.
2. Related Art
Semiconductor memory devices are largely classified into volatile memory devices and nonvolatile memory devices.
In a volatile memory device, a write operation and a read operation are performed at high speeds but stored data is lost when a power cutoff occurs. In a nonvolatile memory device, a write operation and a read operation are performed at relative low speeds but stored data is retained even when a power cutoff occurs. Thus, the nonvolatile memory device is used to store data that should be retained regardless of whether a power cutoff occurs. Examples of the nonvolatile memory device include a read only memory (ROM), a mask ROM (MROM), a programmable ROM (PROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a flash memory, a phase-change random access memory (PCRAM), a magnetic RAM (MRAM), a resistive RAM (ReRAM), a ferroelectric RAM (FRAM), etc. Flash memories are classified into NOR type memories and NAND type memories.
Flash memories have advantages of both a RAM which data can be easily programmed in and erased from and a ROM in which stored data can be retained even when a power cutoff occurs. Flash memories have been widely used as storage media of portable electronic devices such as a digital camera, a personal digital assistant (PDA), and an MP3 player.
Recently, research has been conducted on semiconductor memory devices having a three-dimensional (3D) array structure in order to improve integration degrees of semiconductor memory device. An erase voltage which is a high voltage is applied to such a semiconductor memory device via a source line to perform an erase operation on the semiconductor memory device. In this case, the performance of source selection transistors disposed between the source line and a memory cell may be degraded.